This invention relates to an optical pulse repeater, and more particularly to a light-activated PNPN injection laser diode.
Since at least 1962, when W. P. Dumke demonstrated that lasing is possible in direct band-gap semiconductor material, such as gallium arsenide (see "Interband Transitions and Maser Action," Phys. Rev., Vol. 127, page 1559), there has been great activity in studying and producing a laser action in semiconductor diodes. Once a p-n junction has been properly formed (and forward biased enough for there to be an active region in the vicinity of the junction where the population is inverted) the laser action is produced by stimulated emission upon passing a current through the junction. The mechanism for lasing is the flow of electrons over the top of the junction barrier from the n to the p side where they make transitions to empty electron states in the valence band and emit photons with energy approximately equal to the band gap, E.sub.g. Simultaneously, holes flow to the n side where they recombine with electrons to further produce photons.
The interest in the laser action of p-n junctions has extended to multijunction injection lasers. For example, W. F. Kosonocky, Roy H. Cornely and I. J. Hegyi reported experimental data on the current controlled power output of multijunction GaAs lasers in "Multilayer GaAs Injection Lasers," IEEE Journal of Quantum Electronics, Vol. QE4, No. 4, p. 176, April 1968. See also "The GaAs P-N-P-N Laser Diode" by H. F. Lockwood, et al., IEEE J. Quantum Electronics, Vol. QE 10, No. 7, pp. 567-569, July, 1974. Another more recent investigation is reported in "Radiation Directivity Pattern of a Semiconducting Multilayer Structure" by Yu. P. Demidov, et al, JETP Letters, Vol. 12, No. 4, p. 117, Aug. 1970. Multilayer LED structures have also been investigated, particularly in respect to their operation as light-activated semiconductor-controlled rectifier (SCR) switches. (See Y. Arai, M. Sakuta and K. Sakai, "GaAs Light Emitting Device with Light Activated Negative Resistance, " Japan. J. Appl. Phys., Vol. 9, p. 853, 1970, and D. Meyerhofer, A. S. Keezer and H. Nelson, "A Light-Activated Semiconductor Switch, " J. Appl. Phys., Vol. 38, No. 1, p. 111, January 1967.) The object of the present invention is to provide a monolithic light activated multilayer injection laser useful as an optical pulse repeater or receiver. Such a repeater or receiver must detect weak and dispersed optical pulses arriving through an optical fiber, and then reshape the pulse for retransmission through an optical fiber or for detection and processing. Such a repeater is needed for long distance (kilometers) fiber optics communication.